oa.rf.inverseOperation = new RenderingForm(
  "inverseOperation",
  "Renders four term-result equations for binary addition and multiplication problems and their inverse problems.",
  RenderingModeEL.individually
);
oa.rf.inverseOperation.isApplicableTo = function( apt) {
  if (!(apt instanceof ArithmeticProblemType && 
        apt.numberType === NumberTypeEL.NonNegativeInteger &&
        apt.operators.length === 1 &&
        ( apt.operators[0] === OperatorEL.plus ||
            apt.operators[0] === OperatorEL.times ))) {
    return false;
  } else if (apt.operators[0] === OperatorEL.times) {
    // prevent division by 0
    return (apt.numberRanges[1].lb > 0 && apt.numberRanges[2].lb > 0);
  } else return true;
};
